The present invention refers to a new HIV protease inhibitor compound or salt or prodrug or ester thereof, to the preparation process for this new compound, pharmaceutical composition thereof and therapeutic use of such compound.
Particularly, the compound of the present invention that is a ritonavir analog, has activity for inhibiting HIV protease, an essential enzyme involved in HIV replication process, as shown hereinafter. Consequently, the compound of this invention can be used in HIV infection treatment, itself or in combination with other anti-HIV medicaments.
Human Immunodeficiency Virus (HIV) is a retrovirus (constituted by RNA) belonging to the Lentivirinae subfamily, capable to impair the human immunologic system causing the infectious disease known by the acronym AIDS (Acquired Immuno Deficiency Syndrome) [Pecanha, E. P.; Antunes, O. A. C; Tanuri, A.; Quim Nova, Vol. 25, No. 6B, 1108-1116, 2002].
HIV genome has three main regions: the gag region that codifies inner structural proteins p17, p24, p7 and p6; the pol region that codifies the protease (p11, PR), reverse transcriptase (p66/p51, RT) and the integrase (p31, IN/and, finally the env region, encoding the coating proteins, qp120 and gp41. The HIV-1 genome further encodes six other accessory proteins, wherein two of them (tat and rev) function in regulation of gene expression [Frankel, A. D.; Young, J. A. T.; Annu. Rev. Biochem. 67, 1, 1998].
Cellular infection occurs when HIV virus binds to a cellular receptor, generally the T-cell CD4+ receptor, by means of the gp120 protein; then, virus merges with the cell membrane and the capsid content is released into the cell cytoplasm. The HIV enzyme, reverse transcriptase, catalyses DNA copy production starting from HIV virus RNA. The double helix DNA copy is then transported to the cellular nucleus where a second HIV enzyme, the integrase, catalyses the incorporation of viral DNA to the host genetic material. Subsequent viral gene expression results in RNA transcription starting from HIV DNA and in translation of viral proteins.
However, newly formed viral proteins are produced in the form of polyprotein precursors that are long entities consisting of viral enzymes and structural proteins added to each other. Polyproteins and viral RNA move to the cell surface where they are incorporated into the new viruses that spring from cell membrane taking part of it with them to form the external layer of the viruses.
Newly formed viruses, however, cannot be infectious without the action of a third essential HIV enzyme, the protease, that turns viral polyproteins into functional and structural proteins and enzymes [Nora de Souza, M. V.; Almeida, M. V.; Quim. Nova, Vol. 26, No. 3, 366-373, 2003].
Proteases are enzymes that cleave others proteins at highly specific sites. HIV protease, an aspartyl protease, cleaves viral polyproteins into essential functional proteins during the process of maturation of the “virion” (complete viral particle). This process occurs when each new “virion” springs outside of the infected cell membrane and it continues after the release of immature virus by the cell.
If polyproteins are not cleaved, virus formation does not finish and it becomes unable to infect a new cell. Protease inhibitors, as this name implies, are substances able to inhibit protease enzyme function. They perform their inhibitory effect disabling the enzyme before it cleaves gag/pol polyprotein to form its essential products.
The HIV genome codifies protein precursors known as gag and gag-pol that are processed by viral protease to obtain the protease, reverse transcriptase, integrase and structural proteins of the virus nucleus. Many studies were and still are dedicated to HIV control by the inhibition of the viral coded enzymes. Compounds available nowadays as anti-HIV drugs are capable of inhibiting different phases of viral replication, being classified according to the viral enzymes that they inhibit. They are distributed in three categories: nucleoside-nucleotide reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs).
Particularly, many studies have been dedicated to the inhibition of HIV protease and the protease inhibitors saquinavir, indinavir, ritonavir, nelfinavir, amprenavir and lopinavir are examples of compounds of this category that have been approved by north-American agency of pharmaceutical products control, FDA (“Food and Drug Administration”), for the treatment of HIV infection. Due to resistant strains appearing during monotherapy, the actual treatment of patients includes usage of such protease inhibitors in combination with reverse transcriptase inhibitors. Antiretroviral formulations are commercially available for each agent individually or in the form of combinations of antiretroviral agents.
Although anti-HIV drugs are already available to patients, they are not totally efficient for the disease treatment and/or reversion and many drugs used nowadays for AIDS treatment cause adverse side effects including low platelet count, renal toxicity and bone marrow cytopenia. These factors added to viral resistance to available anti-HIV therapy, demonstrate the necessity of development of new and efficient target-enzyme inhibitors, as well as drugs that act in others stages of viral replication cycle.
One of the requirements for a drug to be considered suitable for a therapeutic use is its therapeutic efficacy. So, to achieve such requirement, the drug should present adequate characteristics of bioabsorption and bioavailability.
Protease inhibitors are high molecular weight substances, normally have lipophilic character, low water solubility and, normally present low absorption and low bioavailability when therapeutically administered in a solid state. Therefore, the development of concentrated pharmaceutical compositions for the administration of these drugs is very difficult and, in addition, high and frequent doses of these substances are necessary to maintain the therapeutic level of the drug inside the body.
The protease inhibitor compound ritonavir (CAS No 155213-67-5), which chemical name is (2S,3S,5S)-5-[N—[N—[[N-methyl-N-[(2-isopropyl-4-thiazolyl)methyl]amino]carbonyl]vanilyl]amino-2-[N [(5-thiazolyl)methoxycarbonyl]amino-1,6-diphenyl-3-hydroxyhexane, is disclosed in PCT document number WO 94/14436 (Kempf, D. J.), as well as several analogous compounds thereof.
Ritonavir presents polymorphism, having a marked difference of solubility between each polymorph. Such characteristic was responsible for discontinuing the first commercial composition in which, along the years, started to present an increasing amount of ritonavir in the form of the less soluble polymorph crystal. Such occurrence harmed the efficacy of HIV suppression of this medicament. Two polymorphs known as polymorph I and polymorph II are disclosed in PCT document WO 00/04016.
As ritonavir presented polymorphic forms with different physical-chemical properties, a new composition, in the form of soft gelatin capsules that suppressed considerably the crystallization of less soluble polymorph, was developed. Such composition, disclosed in document WO 98/22106, is the actual available pharmaceutical composition of ritonavir in the market. However, this composition still presents some disadvantages such as reduced physical-chemical stability, low concentration of ritonavir in each capsule, and very bulky size of the capsules.
In the actual therapy, ritonavir in its commercial pharmaceutical composition in the form of soft gelatin capsules should be administered at a daily dose of 1200 mg, divided in two administrations of 600 mg each. Soft gelatin capsules commercially available contain ritonavir in an amount of 100 mg per capsule. Therefore, a patient in therapy should ingest a total of 12 capsules daily.
Use of ritonavir to inhibit an HIV infection is disclosed in U.S. Pat. No. 5,541,206 (Kempf, D. J.). Use of ritonavir in combination of one or more reverse transcriptase inhibitors to suppress an HIV infection is disclosed in the U.S. Pat. No. 5,635,523 (Kempf, D. J.). Use of ritonavir in combination with one or more HIV protease inhibitors to suppress an HIV infection is disclosed in the U.S. Pat. No. 5,674,882 (Kempf, D. J.).
In the search for new and better anti-HIV drugs, compounds designated as analogous or derivatives of protease inhibitors already approved are commonly found in the literature.
U.S. Pat. No. 5,354,866 (Kempf, D. J.) describes compounds having 1,6-diphenyl-3-hydroxyhexane group in their structure. Such ritonavir derivative compounds include, for instance, the compounds A-83962, A-81525, and A-80987, whose structures are represented below:

wherein, Ph represents a phenyl group.
In other words, this document presents the compound A-83962 in which just the 5-thiazolyl group of the ritonavir is substituted by a 3-pyridinyl group; the compound A-81525 in which (2-isopropyl-4-thiazolyl)-CH2—N(CH3) group of the ritonavir is substituted by the 2-pyridinyl-CH2—O group; and the compound A-80987 in which, compared to ritonavir, the substituted groups in C2 and C5 of the 1,6-diphenyl-3-hydroxyhexane group are inverted, the 5-thiazolyl group is substituted by 3-pyridinyl and the (2-isopropyl-4-thiazolyl)-CH2—N(CH3) group is substituted by 2-pyridinyl-CH2—O.
U.S. Pat. No. 5,541,206 (Kempf, D. J.) refers to retroviral protease inhibitors compounds having a general formula I:

This patent describes substituent groups for each X, Y and R1-R7 radical of formula I and provides examples of combination among the substituents resulting in different compounds, including the protease inhibitor ritonavir (Example 1U, IC50=0.025-0.040 μM) whose structural formula is represented below:
wherein Ph represents a phenyl group. Simple alterations or substituent group additions to the formula I, exemplified by ritonavir, result in different compounds that respond in different ways to the anti-HIV activity test. For instance, the addition of a 2-isopropyl substituent to the 5-thiazolyl ring of ritonavir practically does not alter IC50 value (example 45C, IC50=0.036-0.040 μM), however the substitution of the 2-isopropyl group by 2-isobutyl group at the 4-thiazolyl ring of ritonavir causes a significant increase of the IC50 value (example 59G, IC50=0.11-0.13 μM), in other words the anti-HIV activity decreases. The general formula I does not foresee “(2S,3S,5S)-2,5-Bis-substituted-1,6-diphenyl-3-hydroxyhexane” compounds.
U.S. Pat. No. 5,648,497 (Kempf D. J.) refers to retroviral inhibitor compounds of formula A-X—B, including ritonavir. Among a list of possible variations for X, the formula A-X—B that includes ritonavir and related compounds (having 1,6-diphenyl-3-hydroxyhexane group in their structure), is shown below in a simplified form represented by formula II:

Wherein, for ritonavir:
R1 and R2 are —CH2Ph (Ph is a phenyl group);
A is 5-thiazolyl-CH2—O; and
B is —CH (isopropyl)-NH—C(O)—N(CH3)—CH2-(2-isopropyl-4-thiazolyl)
This patent also describes compounds of formula II in which substituents A-C(O)—NH— and B—C(O)—NH— bonded at C2 and C5, respectively, are inverted in relation to ritonavir. For instance, the compound claimed in this patent wherein A is —CH(isopropyl)-NH—C(O)—N(CH3)—CH2-(2-amino-thiazolyl) and B is 5-thiazolyl-CH2—O, is represented below:
wherein Ph represents a phenyl group. Besides the compounds wherein the substituents A and B in the formula II are inverted, there are also described compounds wherein the substituents A and B are the same, e.g. the compound of the example 79 wherein A=B=(2-methyl-5-thiazolyl)-CH2—O— whose structural molecular formula is shown below:
wherein Ph represents a phenyl group.
Although there are many compounds proved as protease inhibitors or potential inhibitors protected by patents and these documents generally include several variants of these compounds, the knowledge about them and the increasing scientific development can always open possibilities for the investigation and creation of new compounds. As for all new compounds, testing about various aspects from synthesis viability pre-clinical and clinical studies is necessary. There are not complete references in the literature about antiviral activity of several analogous compounds of ritonavir in which were performed the substitution of A group for B group or B group for A group, or still, wherein A group and B group are the same.
Although some 2,5-bis or -di substituted were foreseen in the literature in a generic way, they were not synthesized and/or tested for HIV protease inhibition activity.